The release achieves "parity or better" in terms of quality with the Windows Audio 8 format developed by Microsoft, said Dave Arland, spokesman for Thomson.

Windows' equal MP3pro "dramatically improves sound quality in terms of bit rates", he said. An MP3pro file carries near CD-quality sound recorded at 64Kbps (kilobits per second). This is equal to that of the Windows Audio version, and about half the file size required for the same song in the standard MP3 format.

An MP3 music file recorded at 128Kbps will take up about 1MB per minute of sound. The new codec records two minutes per megabyte without losing fidelity.

CD quality The original MP3 codec discarded some high-pitch sounds in order to prevent encoding errors at low bit-rate recordings, according to Arland. "The result sounded more like a tape recording than a CD," he added. An MP3pro recording uses two tracks, one like the old MP3 and another just for high-frequency sounds. MP3pro improves the high-end frequency response - higher pitches are more distinct.

The new codec is backwards-compatible with MP3 players - an MP3pro player will be able to play MP3 files. However, existing MP3 players will have some trouble with high-pitch sounds on MP3pro files, because the old readers won't play the secondary hi-frequency track.

About 12 million portable devices and 250 million personal computers have an MP3 player. Thomson is negotiating with several companies to use the new format in portable players and music download sites. He claimed: "We're very close on several deals, but nothing that's ready to be announced yet."